Scientists in Israel unveiled a 3D print of a heart with human tissue and vessels on Monday, calling it a first and a “major medical breakthrough” that advances possibilities for transplants.

The heart marked “the first time anyone has successfully engineered and printed an entire heart replete with cells, blood vessels, ventricles and chambers,” said Tel Aviv University’s Tal Dvir, who led the project.

“People have managed to 3D-print the structure of a heart in the past, but not with cells or with blood vessels,” he said.

But the scientists said many challenges remain before fully working 3D printed hearts will be available for transplant into patients.